The present invention relates to apparatus and methods for recording information signals, such as video signals, and tracking control signals with the use of rotary magnetic heads.
In conventional video recording, video signals are recorded on a magnetic tape in successive tracks with the use of a helical scan rotary head assembly. The video signals may be recorded either in analog or digital form, the latter providing improved signal quality upon signal reproduction. In reproducing the signals, it is essential that the slant tracks as recorded are accurately scanned so that the recorded signals are faithfully reproduced. Accordingly, tracking control is employed to ensure that the previously recorded tracks are accurately followed upon reproduction. Digital audio tape (DAT) apparatus typically utilize similar tracking control techniques where the audio signals are recorded in slant tracks.
In one type of tracking control arrangement, proper positioning of the heads with respect to the slant tracks is carried out with the assistance of a control signal recorded along a longitudinal edge of the magnetic tape. This longitudinally recorded control signal is reproduced by a stationary head; and tape movement is adjusted if there is a phase difference between the reproduced control signal and a position signal representing the rotary position of the heads.
However, this technique requires the use of a stationary head which is used for no other purpose. This head adds to the overall cost of the signal recording/playback apparatus and, more importantly, it impedes miniaturization of that apparatus. If the stationary head can be eliminated, the overall size of the apparatus can be reduced correspondingly.
The assignee of the present application has proposed a technique for carrying out tracking control utilizing tracking control signals mixed with information signals in the slant tracks (Japanese patent publication No. 59-112406). This permits the stationary head to be eliminated by utilizing the transducer which reproduces useful information to reproduce the tracking control signals as well. Digital video and digital audio recording are particularly suited for this approach because digital information signals are easily multiplexed with control signals without loss of useful information, they may be time-base compressed easily and they may be readily processed. Accordingly, in a particular track, a tracking control signal may be recorded in a restricted region apart from other regions of the track where digital information signals are recorded.
In one implementation of this proposal, a pilot signal is recorded in the tracks independently of the digital signals. Advantageously, digital video and digital audio signals may be recorded in tracks having no guard bands between them. While this increases the amount of magnetic tape made available to record useful information, it is essential to provide precise tracking control as the playback heads scan the respective tracks. Typically, the heads used for recording and/or reproduction exhibit a gap length larger than the width of a track, which means that an edge of a preceding track is overwritten when the next adjacent track is recorded. This also means that when a playback head is in proper alignment with the pre-recorded track, the signals recorded in both adjacent tracks are picked up as crosstalk components. This phenomenon of crosstalk pickup is used to detect tracking errors and to provide proper tracking control of the scanning heads.
In the arrangement mentioned above, wherein pilot signals of a predetermined frequency are recorded in restricted regions of alternate tracks, a pair of heads having respectively different azimuth angles is used to scan two adjacent tracks substantially simultaneously. Hence, when one head scans the track in which the pilot signal is recorded, the other head scans the adjacent track which has no pilot signal therein. These two heads are mounted on the same rotary head assembly, such as a rotary head drum, and are relatively closely spaced thereon. The head which scans the track having no pilot signal therein will pick up, as a crosstalk component, the pilot signal recorded in an adjacent preceding track as well as the pilot signal recorded in an adjacent following track. If the magnitude of the crosstalk pilot signal picked up by this head from the preceding track is equal to the magnitude of the pilot signal picked up from the following track, the heads are in proper alignment with respect to the tracks scanned thereby. A tracking error is detected if the crosstalk pilot signal magnitudes from the preceding and following tracks differ from each other. In that event, the tape transport is accelerated or decelerated to bring the heads back into proper tracking alignment.
The foregoing technique utilizing a single pilot signal frequency is relatively simple to implement as it uses the constant spacing of the heads for detecting tracking errors. However, alternate tracks are recorded by each of the heads so that the signals of successive tracks have different respective azimuth angles. Upon reproduction, the heads scan respective tracks in which signals are recorded with azimuth angles corresponding to those of the heads. Consequently, the pilot signals are detected as crosstalk by a magnetic head having a different head azimuth angle and their magnitudes, thus, are attenuated. Even though the frequency of the pilot signal is selected to minimize azimuth loss, it is nevertheless relatively difficult to detect such crosstalk pilot signals. This tends to reduce the detection accuracy of the pilot signals and to degrade the tracking control function. The reduction in sensitivity to the pilot signals due to azimuth loss can become significant where the difference in the azimuth angles is large or the track width is narrow.